Radar systems are becoming increasingly common in modern motor vehicles. Radar systems can detect the location of objects around a vehicle and allow the vehicle to respond accordingly. For example, autonomous cruise control (ACC) systems utilize a radar system to detect the location and/or velocity of objects around an automobile. The radar system provides signals corresponding to the detected location and/or velocity to a digital signal processor (DSP), which in response to the signals, automatically adjusts the automobile's speed in order to maintain a safe distance (e.g., if an object is detected in front of the automobile, the DSP sends a signal to the engine or braking system to decelerate).
Radar systems often operate according to a phase monopulse azimuth detection method, which allows for detection of an object's angle and distance relative to a vehicle. The phase monopulse azimuth detection method utilizes two or more receiving antennas to determine the angular position of an object by calculating the phase difference between signals received at each antenna. To distinguish between objects that are at a same distance, but at different angular positions relative to the radar system, digital beam forming (DBF) may be used to generate a radar signal that extends over a small angle.
Typically, DBF radar transmitters comprise a transmission chip configured to generate a radio frequency (RF) signal. The RF signal is provided from the transmission chip to a radar front end for transmission. The front end has a phase shift network, which routes the RF signal through cables of varying length, before the signal is provided to two or more of a plurality of antennas. The frequencies that most radar systems operate at are sufficiently high (e.g., 24 GHz) such that the radar front end cannot be successfully implemented in a same bipolar silicon technology that is used for the transmission chip. Instead, the radar front end is usually implemented as separate monolithic microwave integrated circuits (MMIC) comprising gallium arsenide (GaAs) high electron mobility transistors, for example.